Method for production of metal foam or metal-composite bodies

ABSTRACT

A method for the production of foamable or foamed metal pellets, parts and panels. The method comprises the steps of: i) providing a mixture of a metal alloy powder with a foaming agent powder, ii) pre-compacting the mixture of step i); iii) heating the pre-compacted mixture of step ii) to a temperature below a decomposition temperature of the foaming and at which permanent bonding of the particles occurs v) hot compacting the body for producing a compacted body made of a metal matrix embedding the foaming agent; and vi) reducing the compacted body into metal fragments and thereby obtaining dense foamable metal chips. A method for the production of a foam metal using a closed volume metal shell is also disclosed. The method comprises the steps of: a) providing metal pieces and reducing said metal pieces into smaller metal particles; b) mixing the metal particles with an additive having a decomposition temperature that is greater than a solidus temperature of said metal particles; c) pouring the mixture of step b) into a closed volume metal shell having a given thickness and providing the metal shell with at least one passage for gases to escape; d) reducing the thickness of the metal shell by applying pressure; e) heating the metal shell to a temperature above said solidus temperature of the metal particles and below said decomposition temperature of the additive, and immediately applying pressure on the metal shell sufficient to compress the metal particles and to create micro shear conditions between the metal particles so as to obtain a dense metal product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 10/619,717 filed onJul. 15, 2003, which is a continuation of International PatentApplication No. PCT/CA02/00073 filed on Jan. 16, 2002, which designatesthe United States and claims priority Application Nos. U.S. 60/261,218filed Jan. 16, 2001, CA 2,332,674 filed Jan. 29, 2001 and CA 2,344,088filed Apr. 12, 2001. The above-mentioned applications are incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the field of powder metallurgy. Morespecifically, it concerns a method of manufacturing foamable metal ormetal-composite bodies and their use, particularly as lightweight andstiff material with improved impact, energy, sound absorption and heatretardant properties. It also preferably concerns environmentallyfriendly and low cost material produced from recycled aluminum alloys orscrap with broad range of chemical composition.

BACKGROUND OF THE INVENTION

Already known in the prior art, there is German patent no 4101630 (U.S.Pat. No. 5,151,246) which describes a method for the production ofporous semi-finished products from aluminum and copper-based alloypowders. The method described therein comprises the steps of mixing ofan alloy powder with a foaming agent, filling a press container with themixture, simultaneously heating the filled container and applyingpressure at which the foaming agent does not decompose, simultaneouslycooling and removing the pressure, disassembling of the containerfollowed by pushing of the solid briquette out of it, which isimmediately heat treated to produce a porous body or is subjected topreliminary hot deformation via extrusion or rolling followed by heattreatment. A very narrow range of products in terms of sizes and shapescan be produced with such method since the weight of the briquette is2-5 kg. In addition, this method demonstrates a very low output becauseof the prolonged heating of the large size press container filled withthe powder mixture. Even in the case where the powder mixture would beheated in a container having 100 mm in diameter and 400 mm in height,the heating operation would be economically not feasible.

Also known, there is a method for the production of porous semi-finishedproducts from metallic powders that incorporates different variants.

A first variant includes the steps of coating the bottom floor of apress container with a metallic layer free of foaming agent, coveringthe metallic layer with a powder mixture comprising a foaming agent, andthen covering the layer of powder mixture with a second metallic layerfree of foaming agent. The container is then heated, and hot compactionis carried out. The shape of the body produced can be changed viadeformation. Then, the body is foamed for formation of a new bodywherein a high porous foamed metallic layer appears between two metalliclayers.

A second variant includes the steps of disposing a dense metallic diskin an empty press container adapted for extrusion and filling thecontainer with a powder mixture containing a foaming agent. Then, thecontainer with the powder mixture is subjected to heating followed bythe application of a pressure of about 60 MPa. Due to the pressure, thecentral part of the hard metallic disk, which blocks the hole of thepress die, begins flowing through this hole and ensures extrusionprocess. During subsequent extrusion stages, the compacted powdermixture plastically deforms and flows through the die hole. Also in thiscase, the dense metallic layer covers the extruded powder mixture, whichis ready for foaming. After foaming of this combined body the metalliclayer covers a core consisting of high porous foam.

The combined billets produced via both variants can be further rolled insheets, and due to a heat treatment temperature, can be transformed in aporous metallic body (U.S. Pat. No. 5,151,246, September, 1992, B 22 F3/18, B 22 F 3/24).

Also known in the prior art, there is a process including the steps ofmixing of an alloy powder with a foaming agent and rolling the mixtureat high temperature (in the range of about 400° C. for aluminum) inseveral rolling passes. Intermediate heating of the pre-rolled materialfollowing the individual roll passes is a significant measure to largelyavoid creation of edge cracks. This produces a bonding of metal andpropellant powder particles in the roller nip and forms a gas-tight sealfor the gas particles of the propellant. This body can be transformed byheat treatment in a porous metallic body.

The disadvantages of these techniques are the limited possibility ofproduction of semi-finished products, especially sheets of commercialsizes, low product yield and output, high manufacturing cost.

Also known in the general field of powder metallurgy, there are theprocesses described in EP 0127312 and in U.S. Pat. No. 4,820,141(EP0271095). These documents which do not concern the production of foammetal are given as examples of art related to the present invention.

EP 0127312 discloses a process for the consolidation of metal powdersinto slab configuration in which the metal powder is encapsulated,heated and inserted in a containment die and is subjected to a rollingoperation to consolidate the powder.

U.S. Pat. No. 4,820,141 discloses a method for forming non-equilibriumand/or metastable metallic or non-metallic powder, foil or fine wirematerial into solid body. The method disclosed comprises charging thematerial into a metal container, subjecting the metal containercontaining the material to rolling at a temperature at which theinherent properties of the material are maintained, and thereafterremoving the metal container.

The method of the present invention is distinct from and overcomesseveral disadvantages of the prior art, as will be discussed in detailbelow.

SUMMARY OF THE INVENTION

In accordance with a first aspect, the present invention concerns amethod for the production of metal chips comprising the steps of:

i) providing a mixture of a metal alloy powder with a foaming agentpowder, the foaming agent having a given decomposition temperature abovewhich the foaming agent decomposes into gas, and the powders comprisingfinely dispersed solid particles;

ii) pre-compacting the mixture of step i);

iii) heating the pre-compacted mixture of step ii) to a temperaturebelow the decomposition temperature and at which permanent bonding ofthe particles can occur;

v) hot compacting the mixture obtained in step iii) for producing acompacted body made of a metal matrix embedding the foaming agent; and

vi) reducing the compacted body into metal fragments and therebyobtaining foamable metal chips.

Preferably, the step i) of providing the metal alloy powders and thefoaming agent powder comprises the step of:

disintegrating metal scraps, metal particles or metal chips into themetal alloy powder.

According to one alternative, the method comprises, after step vi), thesteps of:

heating the foamable chips to a temperature below a liquidus temperatureof the metal alloy and sufficient to make the metal chips plastic; and

extruding the heated metal chips for producing a foamable metal wire.

The foamable metal wire obtained can advantageously be cut into smallerfoamable wire segments.

According to a second alternative used for producing porous pellets, themethod preferably comprises, after step vi), the step of:

vii) heating the foamable metal chips obtained in step vi) to atemperature above the decomposition temperature of the foaming agent.

In this second alternative, the method preferably comprises, prior tostep vii) of heating the metal foamable metal chips, the step of mixingsaid foamable metal chips with other powders, for instance refractorymaterial powders. More preferably, prior to mixing the foamable metalchips with the refractory material powders, the method comprises thesteps of heating the foamable metal chips to a temperature below asolidus temperature of the metal alloy and sufficient to make the metalchips plastic; and shaping the metal chips into metal granules, forinstance spherical granules.

The shaping of the metal chips into spherical metal granules preferablycomprises the steps of dispersing the heated chips as a monolayer on aflat heated surface; and applying a heated plate over the monolayer, andshaping the metal chips by simultaneously applying pressure with theheated plate and performing circular movement with the same.

In both alternatives described above, the method may further comprises,after step vi) of disintegrating, the step of classifying the metalchips by grain size. The grain sizes preferably ranges from 1.5 mm to 40mm.

The metal alloy powders used in the process are preferably aluminiumalloy powder. It is however worth noting that any suitable metal alloypowders commonly used in the art, for example copper alloy powders canbe used.

Also preferably, the step of v) of hot compacting is hot rolling.

The present invention also concerns the use of porous metal pellets asdescribed above as fillers for a material selected form the groupconsisting of a polymeric material, a soundproof material, a fireproofmaterial and a shock absorption material.

The polymeric material is preferably a resin and even more particularlyan expandable resin.

According to a second aspect, the present invention also provide amethod for the production of a dense metal product comprising the stepsof:

a) providing metal pieces and disintegrating said metal pieces intosmaller metal particles;

b) mixing the metal particles with an additive having a decompositiontemperature that is greater than a solidus temperature of said metalparticles;

c) pouring the mixture of step b) into a closed volume metal shellhaving a given thickness and providing the metal shell with at least onepassage for gases to escape;

d) increasing the density of the metal shell by applying pressure;

e) heating the metal shell to a temperature above a temperature equal tosaid solidus temperature of the metal particles minus 55° C. more orless 5° C. (for example if the solidus temperature is 480° C., the metalshell will be heated at a temperature above 480° C. minus 55° C., thatis to say above 425° C. more or less 5° C.) and below said decompositiontemperature of the additive, and immediately applying pressure on themetal shell sufficient to compress the metal particles and to createmicro shear conditions between the metal particles so as to obtain adense metal product.

The metal pieces are preferably made of recycled aluminium scraps.Advantages of the process in such case are the following: itsenvironmental friendliness since it uses recycled material, its costeffectiveness since the recycled aluminum scraps are readily availableat low price. Another advantage is the fact that the chemical impuritiescontained in the aluminum metal scraps work as useful additives, whichprovide advantageous predetermined properties to the final product.

The smaller particles of step a) are preferably metal chips or a powderof finely dispersed metal particles.

Preferably, the method comprises prior to step d), the step ofpre-compacting the mixture. More preferably, the pre-compacting isperformed by vibration.

Also preferably, the additive is a foaming agent, preferably selectedfrom the group consisting of TiH₂ and CaCO₃ that decomposes into gas ata temperature greater than the above-mentioned decompositiontemperature. In this case, the method further preferably comprises,after step e), a step of heating the dense metal product, with orwithout the metal shell, to a temperature greater than the decompositiontemperature of the foaming agent, for obtaining a foam metal product.

In step e), the pressure is preferably applied by hot rolling the metalshell. More preferably, the hot rolling is performed with a compressionforce sufficient for obtaining a 95-100% dense metal product.

The closed volume metal shell used in step b) preferably comprises twocontinuous longitudinal main surfaces with side edges, and is deformablein a cross direction. The two longitudinal surfaces can be obtained fromtwo coils of metal strip as will be discussed further below. In thiscase the hot rolling of step e) is preferably performed by at least oneroll moving along one of the surfaces of the shell. Most preferably, theshell is hot rolled between two rolls.

The continuous surfaces are preferably partially closed at their sideedges so as to provide the at least one passage for metal to escape orleaving gases way to escape in longitudinal direction. The partialclosing can made by a process selected from the group consisting ofdiscontinuous welding, bending, clamping and bonding.

Alternatively, the closed volume metal shell can be obtained byproviding a flat or special shape pan with a lid. In this case, step c)comprises the steps of pouring the mixture into the pan and closing thelid of the pan leaving the at least one passage. Such passage(s) can beobtained by discontinuously welding, bending, clamping or bonding thelid to the side walls of the pan or by providing perforation in theshell itself.

The step d), of increasing the density of the metal shell preferablycomprises the step of cold rolling the metal shell.

According to a still preferred embodiment of the invention, the methodincorporates mixing of powder aluminum alloys of various systems:Al—Cu—Mg—Si, Al—Mg—Si, Al—Mg—Cu—Si (cast alloys), Al—Cu—Mg—Mn, Al—Mg—Cu,Al—Zn—Cu—Mg, Al—Zn—Mg—Cu (wrought alloys) with a foaming agent. In onevariant the mixture obtained is filled in a split reusable mould, whichis heated with the powder mixture. Heating of the powder mixture iscarried out at a temperature, which ensures sintering after cooling tothe temperature 10-20° C. below the solidus of most fusible eutectics.As a result, the powder mixture looses its flowability. After removingthe bottom of the mould, the hot mould is placed on the container of avertical press. The ram of this press pushes the sintered powder mixtureout of the mould into the press container, then a dummy-block is placedand hot compaction of the sintered powder mixture is carried out at alow specific pressure to produce porous (86-92% relative density), andeasy breakable briquettes. Using highly efficient machines, the cooledbriquettes are reduced to fragment-shaped chips with powder particles of0.5-5.0 mm in size, chemical composition of which conforms to that ofinitial aluminum alloy powder with uniform distribution of the foamingagent.

The method of the present invention can be used for production of porousmetal bodies for the parts and structural elements used incivil-engineering, machinery, automotive and aircraft and otherindustries wherein combination of such unique properties of thismaterial as high specific strength and rigidity, energy absorption, heatinsulation and sound-proofing, light weight, incombustibility, buoyancyand absolute environmental acceptability are required.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will becomeapparent upon reading the detailed description and upon referring to thedrawings in which FIGS. 1 to 7 are schematic representations of thesequence of steps of a method according to a preferred embodiment of theinvention. The detailed description of each figure is as follows:

FIG. 1 schematically represents the step of mixing of metal powders witha foaming agent powder;

FIG. 2 represents the step of pouring the mixture into a reusable shelland of pre-compacting the mixture by vibration;

FIG. 3 represents the step of sintering;

FIG. 4 represents the step of pushing a sintered briquette from areusable can into press mould;

FIG. 5 represents the step of compaction of the sintered briquette;

FIG. 6 represents the step of reducing the body into foamable chips;

FIG. 7 a represents the step of hot rolling the mixture of powders in aclosed volume metal shell, FIG. 7 b is an enlarged view of the powdermixture at the nip formed by the two rolls, the micro-shear conditionwithin the mixture of powders is illustrated with the arrows;

FIG. 8 is a phase diagram of the powder alloy: Al—Si;

FIG. 9 is a phase diagram of the powder alloy: Al—Mg—Cu—Mn;

FIG. 10 represents the steps of continuous or batch rolling of chips orthe powder mixture in a metal shell formed by two metal strips;

FIG. 11 represents the steps of continuous rolling of chips or thepowder mixture in a metal shell formed by two continuous metal strips;and

FIG. 12 represents the steps of continuous rolling of chips or thepowder mixture in a closed volume metal shell.

While the invention will be described in conjunction with exampleembodiments, it will be understood that it is not intended to limit thescope of the invention to such embodiments. On the contrary, it isintended to cover all alternatives, modifications and equivalents as maybe included as defined by the appended claims.

DESCRIPTION OF PREFERRED EMBODIMENTS

The purpose of the present invention is the production of complex andsimple shape products out of continuous hot-rolled sheets of commercialsizes made from the chips produced from hot-compacted briquettes. Thetechnical result obtained due to realization of the inventionincorporates a dramatic increase in product yield (creation of awaste-free technology), a reduction in manufacturing cost of porousproducts, broadening of the range of products in terms of theirgeometrical sizes, mechanical, thermal and acoustic absorptionproperties and density.

Referring to FIGS. 1 to 6, the method of production of porous productsfrom aluminum alloys incorporates mixing of metal particles (1)including powder, scrap pieces, pellets, bits and/or chips of analuminum alloy containing two or more alloying elements, for example,selected from the group consisting of: Al—Cu—Mg—Si, Al—Mg—Si,Al—Mg—Cu—Si (cast alloys), Al—Cu—Mg—Mn, Al—Mg—Cu, Al—Zn—Cu—Mg,Al—Zn—Mg—Cu (wrought alloys), as well as pure metals (with or withoutadditives) with a powder of a foaming agent (2), the foaming agent (2)having a decomposition temperature exceeding that of solidus of thealuminum alloy powder matrix. The mixture (5) obtained is filled in asplit reusable mould (6) that is heated with the powder mixture (5), asshown in FIG. 3. Heating of the powder mixture (5) is carried out at atemperature that ensures liquid-phase sintering after cooling to 10-20°C. below solidus temperature of the lowest melting point eutectic. As aresult, the powder mixture now in the form of liquid phase sinteredbriquettes (12) loses its flowability. After disassembling of the mould(6), the hot mould is placed on the container (14) of a vertical press.The ram (13) of this press (14) pushes the sintered powder mixture (12)into the press container (14), then dummy-block is placed and hotcompaction of the sintered powder mixture is carried out at a lowspecific pressure, as shown in FIG. 5. The hot-compacted briquettes (15)produced show a density of 86-92 rel. %. These briquettes (15) compactedat a low pressure are porous (8-14 rel. %) and brittle, thus easilybreakable. Referring to FIG. 6, using highly efficient machines, thecooled briquettes (15) are reduced to fragment-shaped chips (18) withchips particles of 0.5-5.0 mm in size, chemical composition of whichconforms to that of initial aluminum alloy powder with uniformdistribution of the foaming agent.

Also preferably, the chips (18) are classified by grain sizes from 1.5up to 40 mm, preferably up to 5 mm, each size fraction is mixed withfine refractory material powders passive to aluminum, then the mixtureis filled in moulds and heated in a furnace up to a foaming temperaturewhich exceeds the liquidus point by 50-70° C.; after completion of thefoaming process, the mixture is screened to separate the refractorymaterial powders from porous chips.

According to another preferred embodiment of the invention, the chipsproduced are classified by grain sizes from 1.5 up to 40 mm, preferablyup to 5 mm, each size fraction is heated up to a temperature below thesolidus point of the alloy by 10-100° C. and then dispersed as amonolayer on a flat heated surface and then the fragment-shaped chipsare pelletized by circular movements of a heated massive disk-shapedplate; then each fraction of the pellets produced is mixed with finerefractory material powders passive to aluminum and then the mixture isfilled in moulds and heated up to a foaming temperature which exceedsthe liquidus point by 50-70° C.; after completion of the foaming processthe mixture is screened to separate spherical porous granules from thefine refractory material powder.

According to a further preferred embodiment, the chips produced areclassified by grain sizes from 1.5 up to 40 mm, preferably up to 5 mmeach size fraction is dispersed as a monolayer on a special base, heatedfrom below up to a temperature of phase transition to liquid state; whenit is examined visually that the foamed pellets reach the desired size,they are removed out of the furnace.

The foamed pellets (also called porous pellets) may then preferably bemixed with a resin and injected into the internal space of anystructural element comprising one or more hollow pieces. The resin iscured to increase stiffness and energy absorption of the structuralelement.

According to another aspect of the invention, the chips which are notscreened to size fraction are used to form a composite block whichcontains a flat metallic sheet with special coating on the surface ofwhich a layer of chips is dispersed and, above this layer, at a certainheight, the second metallic sheet with special coating, stampedbeforehand for the desired component, is located and after this, thecomposite block formed is heated in a furnace up to a foamingtemperature which normally exceeds the liquidus point by at least 50-70°C. and when it is examined visually that the foamed pellets reach theupper metallic layer, the block with foamed powders is removed out ofthe furnace and cooled. (To provide for heating of the block in inertatmosphere).

Preferably in this case, to ensure bracing between the sheets, they arefastened together by connecting crosspieces which simultaneously play arole of fastening connecting elements.

Also preferably, the chips, which are not screened to size fraction, canbe used to fill to the desired volume fraction the internal space of anystructural element comprising one or more hollow pieces. The wholeassembly is heated above a temperature of transition from solid toliquid state of an alloy to form porous filler (core).

According to a further aspect of the invention, the rolling of theheated foamable particles is conducted together and between two or moreheated metal sheets to produce a composite body. The produced compositebody is heated above a temperature of transition from solid to liquidstate of an alloy to form a multi-layer structure with porous core andmetallic bonds between core and facings

FIG. 7 a shows the step of hot rolling a closed volume metal shell (48)enclosing a mixture of small particles of metal (21), preferably metalalloy powders coming from recycled aluminium scrap, and a foaming agentpowder. The metal shell (48) with the mixture is first heated in aheater (50), rolled between two rolls (22) where micro-shear conditionsof the particles occur; and a semi-finished foamable dense product (41)is obtained at the exit of the rolling process. As can be appreciated,in front of the nip (21) formed by the two rolls (22), the mixture ofparticles is substantially loose or flowable. After being processedbetween the rolls (22), the mixture consists of a compacted foamablemixture (16) of powder alloy with foaming agent. This compactedstructure (16) is obtained by subjecting the particles (19) tomicro-shear conditions, such micro-shear conditions being created thanksto the use of the closed volume metal shell (48). As can be appreciated,in the nip formed by the two rolls (22) a zone of plasticity (17) iscreated followed by a zone of elasticity (18). As shown in FIG. 7 b, theparticles (19) in the zone of plasticity (17) are subjected tocompression forces represented with arrow (52) and shear forcesrepresented by arrows (54).

According to a further aspect of the invention shown in FIG. 10, the hotchips, and/or a hot mixture of aluminum powder and a foaming agent, arepoured into a thermostatic feeder (32), where increase in density andmovement of chips and/or mixture is induced by vibration, and rolledbetween two metal strips supplied by coils (36) heated at the furnace(33) to a temperature of about 100° C. higher than the temperature ofthe chips. The produced composite body (41) is heated above atemperature of transition from solid to liquid state of an alloy to forma sandwich structure with porous core and metallic bonds between coreand facings.

According to a further aspect of the invention shown in FIG. 11, the hotchips, and/or a hot mixture of aluminum powder and a foaming agent, arepoured into a thermostatic feeder (32), where increase in density andmovement of chips and/or mixture is induced by vibration, and rolledbetween two continuous metal strips (40) heated at the furnace (33) to atemperature of about 100° C. higher than the temperature of the chips.The hot-rolled sheets (23) produced are cut to blanks, which are fed toa heat treatment.

According to a further aspect of the invention shown in FIG. 12, the hotchips, and/or a hot mixture of aluminum powder and a foaming agent, arepoured into a thermostatic feeder (32), where increase in density andmovement of chips is induced by vibration, then poured on a metal stripfrom the coil (36) moving on a roller table (43). The chips and/ormixture of powder are then covered by an upper metal strip from coil(37), moved to a machine (44) for forming a shell and for joining theedge of the lower and upper metal strips. A closed cross section metalshell (48) filled with chips and/or the mixture of powder is thus formedin that machine (44). The shell is then straightened and density ofchips and/or mixture of powder increased in a straightening machine (45)and heated in a furnace (46). The heated shell is then hot rolled in arolling mill (47). The produced composite body (41) is heated above atemperature of transition from solid to liquid state of the alloyobtained with the original mixture of powder to form a sandwichstructure with porous core and metallic bonds between core and facings.

Alternatively, the metal shell (48) from the shell-forming machine (44)shown in FIG. 12 may be cut to blanks so to form a closed volume metalshell (48). Such closed volume metal shell (48) is then processed, asdescribed above, to be straightened, heated, hot rolled and heated to ahigh temperature to form a sandwich structure with a porous core.

The possibility of realization of the invention characterized by theabovementioned set of the signs and the possibility of the realizationof the purpose of the invention can be corroborated by the descriptionof the following examples.

EXAMPLE 1

The example of the realization of the method for production of densefoamable chips is as follows.

Al—Mg—Cu—Mn aluminum alloy powder (a liquidus temperature of the alloyis 640-645° C., a temperature of low-melting point eutectic is 505° C.)of 300 kg in weight was mixed with TiH₂ foaming agent of 3.25 kg inweight (a decomposition temperature is 690° C. and filled in a splitmould of 340 mm diameter, 800 mm in height with internal space of 290 mmin diameter. FIG. 8 shows a vertical cross section of the phase diagramof Al—Mg—Cu—Mn alloys. Hatched zone in this figure represents alloysused in the process. As can be appreciated, the average solidustemperature is 503° C. and the liquidus temperature is approximately650° C. The powder mixture was compacted by vibration to obtain adensity of 1.75-1.8 g/cm3. Weight of the mixture in each mould was from97 up to 100 kg. The powder mixture was heated at a temperature of510-515° C. to ensure liquid-phase sintering after cooling down to atemperature of 480-485° C., the powder mixture lost its flowability.After disassembling of the mould, the hot mould was placed on thecontainer of a 10 MN or 15 MN capacity vertical press. The diameter andheight of the container were 300 and 800 mm respectively. The ram of thepress pushed the sintered powder mixture into the press container, thena dummy-block was placed and hot compaction of the sintered powdermixture was carried out at a low specific pressure of 140-200 MPa. Thehot-compacted briquettes produced showed a density of 86-92 rel. %.After cooling the briquettes were reduced on special machines tofragment-shaped chips.

Heating of the primary powders above a temperature of appearance oflow-melting point eutectic by 10-20° C. and subsequent cooling belowthis temperature by 20-30° C. ensure development of liquid-phase powdersintering. The powder mixture in this state loses its flowability andcan be easily pushed from the mould into the press container. The firstsource of appearance of extremely low hydrogen amounts is decompositionof TiH₂ at a heating temperature. The second source is surface hydrogenappeared due to reaction of absorbed (H₂O molecules) with aluminumcations which diffuse through an oxide film. Surface hydrogen andhydrogen formed due to decomposition of TiH₂ leave the porous briquettespartially, while the largest hydrogen amount is capable of dissolving inappeared low-melting point eutectic.

Then, hot compaction operation at a low pressure of 140 or 200 MPa iscarried out. Pressure applied to a sintered briquette is able to formonly a porous briquette. The porous state is necessary only tofacilitate production of the chips on special machines. The mainoperation i.e. hot compaction is a waste-free process.

If the heating of the primary powder mixture is performed at atemperature wherein the particles do not bond for example a temperatureof 10-20° C. below that of low-melting point eutectic formation, theparticle will not bond and the powder mixture obtained will retain itsflowability. Transportation of the disassembled mould to the presscontainer will be impossible, a briquette structure will be loose.

EXAMPLE 2

The example of realization of the method for production of poroussemi-finished pellets from the foamable chips is as follows:

Al—Zn—Cu—Mg aluminum alloys powder (a liquidus temperature of the alloyis 630-640° C., a temperature of low-melting point eutectic formation is480° C. of 210 kg in weight was mixed with CaCO₃ foaming agent of 12 kgin weight (a decomposition temperature is 720° C.) and filled in a splitmould of 340 mm in diameter, 800 mm in height with internal space of 290mm in diameter. FIG. 9 shows surfaces of crystallization (surfaces ofliquidus) of the powder alloy Al—Zn—Cu—Mg containing Zn-4, 5%, Cu3.5-4.5%, Mg-negligible, Al-balance. The alloys used are in the ALcorner of the diagram (small hatched zone) and have a liquidustemperature of 650° C. Solidus of these alloys is in the interval oftemperatures of 510-520° C. The powder mixture was compacted byvibration to obtain a density of 1.75-1.8 g/cm³. Weight of the mixturein each mould was from 97 up to 100 kg. The powder mixture was heated ata temperature of 490-500° C. to ensure liquid-phase sintering aftercooling down to 450-460° C. and the mixture lost its flowability. Afterdisassembling of the mould, the hot mould was placed on the container ofa 10 MN or 15 MN capacity vertical press. The diameter and height of thecontainer were 300 and 800 mm respectively. The ram of the press pushedthe sintered powder mixture into the press container, then a dummy-blockwas placed and hot compaction of the sintered powder mixture was carriedout at a low specific pressure of 140-200 MPa. The hot-compactedbriquettes produced showed a density of 86-92 rel. %. After cooling, thebriquettes were reduced on special machines to fragment-shaped chips.

To realise the method, the chips produced were graded into grain sizesof 2.0, 3.0, 4.0 and 5.0 mm, each size fraction was mixed with finerefractory material powders passive to aluminium, the mixture was filledin moulds, heated in a furnace at a foaming temperature which exceedsthe transition temperature from solid to liquid state by 50-70° C.;after completion of the foaming process, the mixture was screened toseparate the refractory material powders from porous pellets. The porouspellets from 3.0 up to 10.0 mm in size and 0.3 up to 0.9 g/cm3 indensity are a good filling agent for any shape of cases for energyabsorbing components used in the automotive industry.

An easier technique for realization of the chips of the same alloy,graded into grain sizes of 2.0, 3.0, 4.0 and 5.0 mm is discussed below.Each fraction was dispersed as a monolayer on a special base, heated ina furnace from below on overheated melt of salt up to a foamingtemperature; when it was examined visually that the foamed pelletsreached the desired size, they were removed out of the furnace andcooled. The pellets had a hemispheric shape with radius from 5.0 up to20.0 mm and a density from 0.4 up to 1.0 g/cm3.

Porous pellets of this size and shape can find application forproduction of volumetric noise suppression and fire barrier componentsand also large-size shock absorption elements. Product yield is 100%.

EXAMPLE 3

An example of the realization of the method for production of flatporous semi-finished products is as follows.

Al—Mg—Cu—Mn aluminum alloy powder (a liquidus temperature of the alloyis 640-645° C., a temperature of low-melting point eutectic is 505° C.)of 30 kg in weight was mixed with TiH₂ foaming agent of 0.32 kg inweight and filled in 10 closed volume metal shells with length 500 mm,width 120 mm and thickness 10 mm. The powder mixture was compacted byvibration and a pass through the straightening machine to obtain adensity of 1.8-2.0 g/cm3. Weight of the mixture in each shell was from2.9 up to 3.2 kg. Then the powder mixture in a shell was heated at ahigh rate in a furnace to a temperature 515-550° C. and fed on a rollingmill on which 29 kg of 120×1000×5 mm blanks with metal facing andfoamable core were rolled. The blanks were used for free foaming ofsandwich panels. High-temperature heat treatment was carried out byheating of the sheet blanks from below on overheated melts of salts. Atthe required point, the foaming process was stopped by quick removal ofthe foamed sandwich panel from the furnace when thickness was 24.5 mm.The size of the panel with porous core was 122×1005×24.5 mm. The lowerand upper surface of the panels was smooth. The density of the poroussemi-finished products produced was 0.96-1.07 g/cm3. Panels yield was95%.

Although preferred embodiments of the present invention have beendescribed in detail herein and illustrated in the accompanying drawings,it is to be understood that the invention is not limited to theseprecise embodiments and that various changes and modifications may beeffected therein without departing from the scope or spirit of thepresent invention.

1-32. (canceled)
 33. A method for the production of a metal productcomprising the steps of: introducing a mixture comprising metalparticles and an additive having a decomposition temperature that isgreater than a solidus temperature of said metal particles into a closedvolume metal shell having a given thickness and providing the metalshell with at least one passage for gases to escape; increasing thedensity of the metal shell with metal particles and additive by applyingpressure; and heating the metal shell to a temperature above atemperature equal to said solidus temperature minus 50-60 degreesCelsius and below said decomposition temperature of the additive, andimmediately applying pressure on the metal shell sufficient to compressthe metal particles and to create micro shear conditions between themetal particles so as to obtain a dense metal product.
 34. The method ofclaim 33, further comprising pre-compacting the mixture beforeincreasing the density of the metal shell with metal particles andadditive.
 35. The method of claim 34, wherein pre-compacting of themixture is performed by vibration.
 36. The method of claim 33, whereinthe pressure is applied to said metal shell by hot rolling the metalshell.
 37. The method of claim 36, wherein the hot rolling is performedwith a compression force sufficient for obtaining a 95-100% dense metalproduct.
 38. The method of claim 33, wherein the closed volume metalshell comprises two continuous longitudinal main surfaces with sideedges, and is deformable in a cross direction.
 39. The method of claim38, wherein the continuous surfaces are at least partially closed attheir side edges, said partial closing being made by a process selectedfrom the group consisting of welding, bending, clamping and bonding. 40.The method of claim 38, wherein the hot rolling is performed by at leastone roll moving along one of said surfaces of the shell.
 41. The methodof claim 33, wherein the closed volume metal shell is obtained byproviding a flat pan with a lid; and wherein the mixture is introducedinto the pan and closing the lid of the pan leaving said at least onepassage.
 42. The method of claim 33, wherein increasing the density ofthe metal shell comprises cold rolling the metal shell.
 43. The methodof claim 33, wherein the metal particles comprises recycled aluminiumscraps.
 44. The method of claim 33, wherein the metal particles aremetal chips, a powder of finely dispersed metal particles, agglomeratedpowders, particles, or mixtures thereof.
 45. The method of claim 33,wherein the additive comprises a foaming agent that decomposes into gasat a temperature greater than said decomposition temperature.
 46. Themethod of claim 45, wherein the dense metal product obtained consistsessentially in a dense foamable metal product comprising said metalparticles and said foaming agent.
 47. The method of claim 45, whereinthe dense metal product obtained is a sandwich structure metal productcomprising a dense foamable metal core comprising metal particles andsaid foaming agent; and two metal facings.
 48. The method of claim 47,wherein said metal facings are made of said metal shell.
 49. The methodof claim 47, wherein said product comprises metallic bonds between saidcore and said facings.
 50. The method of claim 45, wherein the foamingagent is chosen from TiH₂, CaCO₃, and a mixture thereof.
 51. The methodof claim 45, further comprising the step of heating the dense metalproduct to a temperature greater than the decomposition temperature ofthe foaming agent, for obtaining a foam metal product.
 52. The method ofclaim 51, wherein the foam metal product obtained consists essentiallyin a porous metal product comprising said metal particles.
 53. Themethod of claim 51, wherein the foam metal product obtained is asandwich structure metal product comprising a porous metal corecomprising metal particles; and two metal facings.
 54. The method ofclaim 53, wherein said metal facings are made of said metal shell. 55.The method of claim 54, wherein said product comprises metallic bondsbetween said core and said facings.
 56. A dense foamable metal productobtained by a method as defined in claim
 45. 57. A dense foamable metalproduct obtained by a method as defined in claim
 47. 58. A densefoamable metal product obtained by a method as defined in claim
 48. 59.A foam metal product obtained by a method as defined in claim
 52. 60. Afoam metal product obtained by a method as defined in claim
 53. 61. Asandwich structure metal product comprising a dense foamable corecomprising metal particles and a foaming agent; and two metal facings,said product being characterized in that it comprises metallic bondsbetween said core and said facings.
 62. A sandwich structure metalproduct comprising a porous metal core; and two metal facings, saidproduct being characterized in that it comprises metallic bonds betweensaid core and said facings.